Acoustic Velocity with Temperature and AppleScript

NOTE: visit for the current code version.

UPDATE – additional user prompt to enter the measured distance (in feet) between the reference speaker and delay speaker. This version will round all returned values to two decimal places, for convenience. If you require a more precise measurement, you can delete the rouding functions in the final “display dialog” line.

ORIGINAL – On a recent job I had to calculate acoustic velocity to set speaker delays without access to a true RTA. I’m not a big fan of the one-millisecond-per-foot “rule” for anything other than quick mental calculations independent of production conditions. I would rather be more accurate. So, utilizing the following equation to calculate acoustic velocity based on measured temperature in degrees Celsius:

Acoustic Velocity (m/s) = 331.4m/s + (0.6 * temperature Celsius)

I use a digital temperature meter to get degrees Fahrenheit (a better measurement for calculations in the States) and convert as follows:

(Degrees Fahrenheit – 32) * 5/9 = Degrees Celsius

Plug the Celsius value into the equation above to return acoustic velocity in m/s based on measured temperature (because as we know, air temperature determines acoustic velocity).

Then, put that measurement into something more useful, like ft/ms, which is what a standard speaker processor will be looking for.

Take your m/s value and multiply by 0.00328084

Once you know the distance in feet between your zero reference and your delay speaker, multiply that by the ft/ms value above to get your ms offset for the delay. Of course, this will not be perfectly accurate as it can’t take into account air density, just temperature. For indoor use, it’s still pretty good and certainly better than one-millisecond-per-foot.

To make the whole process a bit easier, I wrote some AppleScript that prompts for a temperature value, then returns acoustic velocity in m/s and ft/ms.

Source available at